Display apparatus and head mounted display

ABSTRACT

A display apparatus includes a light guide element, and an incident optical system causing light coming from a display element to enter the light guide element that includes a first light guide part guiding the light coming from the incident optical system in a first direction and a second light guide part guiding the light coming from the first light guide part in a second direction intersecting with the first direction. The first light guide part has mirrors disposed along the first direction and guiding the light to the second light guide part by reflecting the light. The mirrors include a first mirror and a second mirror, each having a first reflection region and a second reflection region having a higher reflectance than the first reflection region. Light having transmitted through the first reflection region of the first mirror enters the second reflection region of the second mirror.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of International Patent ApplicationNo. PCT/JP2018/044675, filed Dec. 5, 2018, which claims the benefit ofJapanese Patent Application No. 2017-235480, filed Dec. 7, 2017, both ofwhich are hereby incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a display apparatus and a head mounteddisplay and, more specifically, to a display apparatus using a lightguide plate.

Description of the Related Art

A display apparatus using a light guide plate guides light emitted froma display element to a viewer's eye with the light guide plate anddisplays an image to the viewer's eye.

Japanese Patent Application Laid-Open No. 2005-521099, Japanese PatentApplication Laid-Open No. 2010-533316, and international Publication No.WO2015/076335 describe display apparatuses that display an image byenclosing light coming from a display element within a planar substrateand outputting the light with a plurality of output mirrors.

In Japanese Patent Application Laid-Open No. 2005-521099, JapanesePatent Application Laid-Open No. 2010-533316, and InternationalPublication No. WO2015/076335, the plurality of output mirrors is used.Here, the width of each of deflected beams deflected by the outputmirrors reduces, and there is a significant gap between the adjacentbeams. As a result, the display apparatuses described in thesepublications cannot display high-quality images.

Japanese Patent Application Laid-Open No. 2003-520984 describes that thewidth of each of deflected beams is increased by using mirrors eachhaving a plurality of regions with different reflectances. JapanesePatent Application Laid-Open No. 2003-520984 describes a displayapparatus that expands the width of a beam in a one-dimensionaldirection; however, it does not provide any disclosure about a displayapparatus that expands the width of a beam in two-dimensionaldirections.

In addition, Japanese Patent Application Laid-Open No. 2003-520984 doesnot describe the use of a polarization beam splitter.

SUMMARY OF THE INVENTION

Embodiments of the invention provide a display apparatus that is able todisplay further high-quality images.

A display apparatus according an aspect of the present inventionincludes a light guide element and an incident optical system configuredto cause light coming from a display element to enter the light guideelement. The light guide element includes a first light guide partconfigured to guide the light coming from the incident optical system ina first direction and a second light guide part configured to guide thelight coming from the first light guide part in a second directionintersecting with the first direction. The first light guide part has aplurality of mirrors disposed along the first direction and configuredto guide the light to the second light guide part by reflecting thelight. The plurality of mirrors includes a first mirror and a secondmirror. Each of the first and second mirrors has a first reflectionregion and a second reflection region having a higher reflectance thanthe first reflection region. Light having transmitted through the firstreflection region of the first mirror enters the second reflectionregion of the second mirror.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a display apparatus of a firstembodiment to which the present invention is applicable.

FIG. 2 is a perspective view of a light guide plate of the firstembodiment to which the present invention is applicable.

FIG. 3A is a diagram that illustrates a horizontal light guide part ofthe first embodiment to which the present invention is applicable.

FIG. 3B is a diagram that illustrates the horizontal light guide part ofthe first embodiment to which the present invention is applicable.

FIG. 3C is a diagram that illustrates the horizontal light guide partaccording to the first embodiment of the present invention.

FIG. 4A is a diagram that illustrates a horizontal mirror set of thefirst embodiment to which the present invention is applicable.

FIG. 4B is a diagram that illustrates the horizontal mirror set of acomparative example.

FIG. 4C is a diagram that illustrates the horizontal mirror set of thefirst embodiment to which the present invention is applicable.

FIG. 4D is a diagram that illustrates the horizontal mirror set of thefirst embodiment to which the present invention is applicable.

FIG. 5A is a diagram that illustrates a vertical light guide part of thefirst embodiment to which the present invention is applicable.

FIG. 5B is a diagram that illustrates the vertical light guide part ofthe first embodiment to which the present invention is applicable.

FIG. 6 is a diagram that illustrates vertical output mirrors of thefirst embodiment to which the present invention is applicable.

FIG. 7 is a diagram that illustrates the horizontal mirror set of thefirst embodiment to which the present invention is applicable.

FIG. 8 is a perspective view of a display apparatus of a secondembodiment to which the present invention is applicable.

FIG. 9A is a diagram that illustrates a horizontal light guide part ofthe second embodiment to which the present invention is applicable.

FIG. 9B is a diagram that illustrates the horizontal light guide part ofthe second embodiment to which the present invention is applicable.

FIG. 9C is a diagram that illustrates the horizontal light guide partaccording to the second embodiment to which the present invention isapplicable.

FIG. 10 is a diagram that illustrates a vertical light guide part of thesecond embodiment to which the present invention is applicable.

FIG. 11A is a diagram of a display apparatus of a third embodiment towhich the present invention is applicable.

FIG. 11B is a diagram of the display apparatus of the third embodimentto which the present invention is applicable.

FIG. 12 is a perspective view of smartglasses of a fourth embodiment towhich the present invention is applicable.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the attached drawings.

First Embodiment

A display apparatus of a first embodiment to which the present inventionis applicable will be described.

FIG. 1 shows the display apparatus of the first embodiment to which thepresent invention is applicable. In the following description that willbe made with reference to the drawings, reference numeral 1 denotes thedisplay apparatus, reference numeral 2 denotes a light guide plate(light guide element), reference numeral 3 denotes an incident opticalsystem, reference numeral 4 denotes a display element, reference numeral5 denotes a viewer's eye, reference numeral 21 denotes a horizontallight guide part (first light guide part), and reference numeral 22denotes a vertical light guide part (second light guide part). Referencenumeral 211 denotes a horizontal propagation part (first propagationpart reference numeral 212 denotes a horizontal mirror set (first mirrorset), reference numeral 221 denotes a vertical propagation part (secondpropagation part), reference numeral 222 denotes a vertical mirror set(second mirror set), reference numeral 2113 denotes a top surface (firstreflection surface), and reference numeral 2114 denotes a bottom surface(first exit surface). Reference numeral 2211 denotes a front surface(second exit surface), reference numeral 2212 denotes a rear surface(second reflection surface), reference numeral 2120 denotes horizontaloutput mirrors (a plurality of mirrors), reference numeral 2121 denotesa first reflection region (half mirror), and reference numeral 2122denotes a second reflection region (high-reflectance mirror).

The display apparatus 1 includes the light guide plate (light guideelement) 2, the incident optical system 3, and the display element 4.

Diverging beams emitted from the display element 4 are converted toparallel beams by the incident optical system 3 and coupled to anincident surface of the light guide plate 2. The coupled beams propagateinside the light guide plate 2, then exit from an exit surface of thelight guide plate 2, and enter the viewer's eye 5. In this way, thedisplay apparatus 1 of the present embodiment is a display apparatusthat is able to display images (including video) to the viewer's eye 5when the viewer puts the eye 5 at a predetermined position on the exitsurface side of the light guide plate 2. Examples of the display element4 include a transmissive liquid crystal display (LCD), a reflectiveliquid crystal display (LCOS), a digital mirror device (DMD), an organicelectroluminescence (OLED), and a spatial light modulation apparatus(SLM).

FIG. 2 shows the light guide plate of the present embodiment.

The light guide plate 2 of the present embodiment has the horizontallight guide part 21 through which beams propagate inside the light guideplate 2 in a horizontal direction (first direction) and the verticallight guide part 22 through which beams propagate inside the light guideplate 2 in a vertical direction (second direction). The horizontal lightguide part 21 has the horizontal propagation part 211 and the horizontalmirror set 212. The horizontal mirror set 212 is disposed on the lowerside of the horizontal propagation part 211. The vertical light guidepart 22 has the vertical propagation part 221 and the vertical mirrorset 222. The vertical mirror set 222 is disposed on a side of thevertical propagation part 221, on which the viewer's eye 5 is placed.The horizontal light guide part 21 is coupled to the vertical lightguide part 22 by placing the vertical propagation part 221 on the lowerside of the horizontal mirror set 212. Thus, the light guide plate 2 isformed.

FIG. 3A is a top view of the horizontal light guide part. FIG. 3B andFIG. 3C each are a front view of the horizontal light guide part.

FIG. 3A and FIG. 3B also show how beams that pass through the center ofan angle of view (beams that exit parallel to an X direction from thelight guide plate), that is, beams at the center of the angle of view,for the viewer's eye propagate inside the horizontal light guide part.

Beam propagation inside the horizontal light guide part will bedescribed with reference to FIG. 3A and FIG. 3B.

The horizontal light guide part 21 includes the horizontal propagationpart 211 and the horizontal mirror set 212. The horizontal light guidepart 21 is formed by joining part of the bottom surface 2114 of thehorizontal propagation part 211 with a top surface of the horizontalmirror set 212. At this joint surface, that is, between the horizontalpropagation part 211 and the horizontal mirror set 212, a transmissivereflection film that passes part of incident beams and reflects part ofthe beams is disposed.

The horizontal propagation part 211 is a cube having a front surface2111, a rear surface 2112, the top surface 2113, the bottom surface2114, a left surface 2115, and a right surface 2116. Where the length isL, the height is H, and the width is W, the length L is the greatest,the height H is the second greatest, and the width W is the least. Thehorizontal propagation part 211 is a cuboid having a long side in ahorizontal direction (Z-axis direction) and is disposed such that thetop surface 2113 faces in a Y direction where the vertical light guidepart 22 is disposed. The horizontal mirror set 212 is disposed so as toface the top surface 2113 (first reflection surface) of the horizontalpropagation part 211.

The left surface 2115 of the horizontal propagation part 211 is used asan incident surface, and beams coming from the incident optical system(not shown) enter from the incident surface. A region of the bottomsurface 2114 (first exit surface) of the horizontal propagation part211, joined with the horizontal mirror set 212, is used as an exitregion, and light having passed through at least part of the horizontalpropagation part 211 exits from the exit region. Beams at the center ofthe angle of view of incident beams enter the horizontal propagationpart 211 at four angles, that is, ±26 degrees in an X-Z cross-sectionaldirection and ±32 degrees in a Y-Z cross-sectional direction, withrespect to an axis (long axis) Ax of the horizontal propagation part 211in the longitudinal direction and become propagating beams inside thehorizontal light guide part 21. The reason why beams at the center ofthe angle of view enter at four angles with positive and negativeinclinations in each of the X-Z cross-sectional direction and the Y-Zcross-sectional direction will be described in detail later withreference to FIG. 9A and FIG. 9B of a second embodiment. The reason willbe simply described here. Planar parts (not shown) respectively parallelto the rear surface 2112 and the top surface 2113 are provided at aconnection part 32 of the incident optical system 3, connected to thehorizontal light guide part 21. A beam that is internally reflected bythe planar parts and enters the horizontal light guide part 21 and abeam that is not internally reflected by the planar parts and enters thehorizontal light guide part 21 appear in each of the X-Z cross-sectionaldirection and the Y-Z cross-sectional direction, so beams enter at fourangles. In the present embodiment, the incident optical system 3 and thehorizontal light guide part 21 are made of the same material, and,inside the horizontal light guide part 21, propagating beams have anglesof ±26 degrees in the X-Z cross-sectional direction and ±32 degrees inthe Y-Z cross-sectional direction with respect to the long axis Ax. Atthis time, the angles that the propagating beams make with respect tothe long axis Ax are termed X-Z propagation angles in the X-Zcross-sectional direction and Y-Z propagation angles in the Y-Zcross-sectional direction.

In FIG. 3A, propagating beams 511, 513 are beams having an X-Zpropagation angle of +26 degrees, propagating beams 512, 514 are beamshaving an X-Z propagation angle of −26 degrees, and those propagatingbeams repeat total reflection on the front surface 2111 and the rearsurface 2112 and reach the right surface 2116.

In FIG. 3B, the propagating beams 511, 512 are beams having a Y-Zpropagation angle of +32 degrees, the propagating beams 513, 514 arebeams having an X-Z propagation angle of −32 degrees, and thosepropagating beams repeat total reflection on the top surface 2113 andreflection on the bottom surface 2114 and reach the right surface 2116.

In this way, propagating beams at all the angles of view, including thebeams at the center of the angle of view, propagate inside thehorizontal propagation part 211 at angles in two-dimensional directions(the X-Z cross-sectional direction and the Y-Z cross-sectionaldirection), and propagating beams are configured to propagate spirallyinside the horizontal propagation part 211.

Propagating beams propagate in the horizontal direction to the rightsurface 2116 while repeating internal reflection on four surfaces (thefront surface 2111, the rear surface 2112, the top surface 2113, and thebottom surface 2114) of the horizontal propagation part 211, parallel tothe horizontal direction. Propagating beams having reached the bottomsurface 2114 of the horizontal propagation part 211 are partiallyreflected by the transmissive reflection film provided at the jointsurface and partially pass through, and the propagating beams havingpassed through the joint surface enter the horizontal mirror set 212.The plurality of horizontal output mirrors 2120 having inclinations inthe Y-Z cross section is disposed so as to be arranged in the Z-axisdirection in the horizontal mirror set 212. Propagating beams havingentered the horizontal mirror set 212 are reflected by the horizontaloutput mirrors 2120 to be deflected to the Y-axis direction, and enterthe vertical light guide part 22.

As described above, in the present embodiment, propagation angles arethe positive direction and the negative direction in each of the X-Zcross-sectional direction and the Y-Z cross-sectional direction for oneangle of view, and four directions in total. With this arrangement, thehorizontal propagation part 211 can be filled with propagating beams, soa light quantity distribution of beams that enter a viewer's eye can bemade uniform even when propagating beams are output from any position ofthe horizontal propagation part 211.

Although not shown in the drawing, for propagation angles inside thehorizontal light guide part 21, a beam at each angle of view has anangle of 0 degrees to ±7.7 degrees in the X-Z cross-sectional directionand 0 degrees to ±13.5 degrees in the Y-Z cross-sectional direction withrespect to a beam at the center of the angle of view. When a beam exitsfrom a light guide plate having a refractive index N=1.4 or higher and2.0 or lower into an air layer having a refractive index N=1.0 andenters a viewer's eye, the light refracts at the exit surface, so theangle of view is greater than the propagation angle. The displayapparatus has a vertical angle of view of 0 degrees to ±11.6 degreesconverted from the X-Z propagation angle since the X-Z cross-sectionaldirection is the vertical direction and has a horizontal angle of viewof 0 degrees to ±20.0 degrees converted from the Y-Z propagation anglesince the Y-Z cross-sectional direction is the horizontal direction.

A propagation angle ω in the horizontal propagation part 211 and anincident angle Ψ to the side surfaces (the top surface, the bottomsurface, the front surface, and the rear surface) of the horizontalpropagation part 211 have the relationship expressed by ω=90 degrees−Ψ.When a propagation angle of a propagating beam inside the horizontalpropagation part 211 is set to a greater value, light is not totallyreflected on the side surfaces of the horizontal propagation part 211and passes through the side surfaces depending on the refractive indexof the material of the horizontal propagation part 211. For example whenthe material of the horizontal propagation part 211 is synthetic quartz(Nd=1.45857), a critical angle is 43.28 degrees, and light passesthrough the side surfaces of the horizontal propagation part 211 at apropagation angle of ω=90 degrees−43.28 degrees=46.72 degrees orgreater.

In the present embodiment, a beam is propagated in the two-dimensionaldirections inside the horizontal propagation part 211, so a resultantincident angle in the two-dimensional directions to the side surfaces ofthe horizontal propagation part 211 can be increased as compared to whena beam is propagated in one-dimensional direction. A propagation angle ωinside the horizontal propagation part 211 may be the range of aconditional expression (1).

10 degrees≤ω≤50 degrees  Conditional Expression (1)

When the propagation angle ω exceeds the upper limit, incident angles tothe side surfaces of the horizontal propagation part 211 are less thanthe critical angle depending on a material. When the propagation angle ωbecomes less than the lower limit, many gaps appear in the deflectedbeams reflected by the horizontal mirror set 212. The latter case willbe described in detail later with reference to FIGS. 4A to 4D.

In the present embodiment, within the horizontal propagation part 211,propagation angles (X-Z propagation angles ωxz) in the X-Zcross-sectional direction are +18.3 degrees to +33.7 degrees, and −18.3degrees to −33.7 degrees, and propagation angles (Y-Z propagation anglesωyz) in the Y-Z cross-sectional direction are +18.5 degrees to +44.5degrees, and −18.5 degrees to −44.5 degrees. An X-Z propagation angle inone-dimensional direction or a Y-Z propagation angle in one-dimensionaldirection can be set to “90 degrees−(Critical angle)” or greater withinthe range in which a propagation angle ω in two-dimensional directionsis less than “90 degrees−(Critical angle)”, and beams having a wideangle of view can be propagated while a loss in light quantity isreduced.

FIG. 3C shows how beams at angles of view propagate.

A beam at each angle of view will be described with reference to FIG.3C.

In FIG. 3C, a beam 511 at an angle of view propagates inside thehorizontal propagation part 211 at a Y-Z propagation angle of ±32degrees, a beam 523 at an angle of view propagates inside the horizontalpropagation part 211 at a Y-Z propagation angle of −45 degrees, and abeam 533 at an angle of view propagates inside the horizontalpropagation part 211 at a Y-Z propagation angle of −19 degrees. Apropagating beam at each angle of view has propagation angles in apositive direction and a negative direction, and FIG. 3C shows one ofthem.

The propagating beams 511, 523, 533 propagate while repeating internalreflection (total reflection) on the top surface, front surface, andrear surface of the horizontal propagation part 211 and internalreflection (partial reflection) on the bottom surface of the horizontalpropagation part 211. When a propagating beam reaches the bottom surface2114 to which the transmissive reflection film is applied, part of thepropagating beam transmits through the bottom surface 2114 and entersthe horizontal mirror set 212, and another part reflects on the bottomsurface 2114 and propagates inside the horizontal propagation part 211.

The output mirrors 2120 having inclinations in the Y-Z cross-sectionaldirection are disposed in the horizontal mirror set 212. Light havingentered the horizontal mirror set 212 is reflected by the output mirrors2120, and the propagation angle in the Y-Z cross-sectional direction isdeflected. Then, the light transmits through the bottom surface of thehorizontal mirror set 212 and enters the vertical light guide part 22.

At this time, since the horizontal mirror set 212 is placed on thevertical light guide part 22 side of the horizontal propagation part211, the number of times of reflection at the time of propagation insidethe horizontal propagation part 211 is reduced, so a loss in lightquantity is reduced.

This will be described in detail. When the viewer sees straight ahead,beams that exit from the center of the vertical light guide part 22 ofthe light guide plate 2 in the horizontal direction (Z-axis direction)reach the viewer's eye to show an image. When the viewer sees to theleft, beams exiting from the left side of the vertical light guide part22 reach the viewer's eye to show an image. When the viewer sees to theright, beams exiting from the right side of the vertical light guidepart 22 reach the viewer's eye to show an image. In FIG. 3C, the beam511 has a Y-Z propagation angle of +32 degrees, and the beam reflectedby the horizontal mirror set 212 travels straight downward in the Y-Zcross section and corresponds to a beam that travels at the center ofthe angle of view for the eye. The beam 523 has a Y-Z propagation angleof −45 degrees, and the beam reflected by the horizontal mirror set 212travels to the lower right in the Y-Z cross section and corresponds to abeam that travels at the left side of the angle of view for the eye. Thebeam 533 has a Y-Z propagation angle of −19 degrees, and the beamreflected by the horizontal mirror set 212 travels to the lower left inthe Y-Z cross section and corresponds to a beam that travels at theright side of the angle of view for the eye. Therefore, when the beam511 exits from around the center of the horizontal mirror set 212, thebeam 511 becomes an effective beam that enters the viewer's eye. Whenthe beam 523 exits from the left side of the horizontal mirror set 212(the horizontal propagation part left surface 2115 side), the angle ofview beam 523 becomes an effective beam that enters the viewer's eye.When the beam 533 exits from the right side of the horizontal mirror set212 (the horizontal propagation part right surface 2116 side), the beam533 becomes an effective beam that enters the viewer's eye. In this way,a beam having a greater absolute value of the propagation angle becomesan effective beam when the beam exits from the horizontal propagationpart incident surface (left surface 2115) side of the horizontal mirrorset 212. When the absolute value of the propagation angle is large, thenumber of times of reflection inside the horizontal propagation part 211for a propagation distance increases, and the number of times ofreflection at the time of propagating to a position where the beambecomes an effective beam increases, with the result that a loss inlight quantity arises. Particularly, the transmissive reflection film isinstalled at the joint surface between the bottom surface 2114 of thehorizontal propagation part 211 and the horizontal mirror set 212 andthe reflectance at the joint surface (or a joint region at the bottomsurface 2114 of the horizontal propagation part 211) is about 50%, thelight quantity of a propagating beam decreases with the number of timesof reflection. This results in that the light quantity of a propagatingbeam decreases as the position of the propagating beam becomes fartherfrom the incident surface 2115 of the horizontal propagation part 211;however, to make the light quantity distribution uniform in all theangles of view, light quantities are adjusted to a lower light quantity,so a loss in light quantity is problematic.

As in the case of the present embodiment, when the horizontal mirror set212 is disposed between the horizontal propagation part 211 and thevertical propagation part 221, beams having a greater absolute value ofthe propagation angle become effective beams when the beams exit fromthe horizontal propagation part incident surface 2115 side of thehorizontal mirror set 212. Thus, the number of times of reflectioninside the horizontal propagation part 211 is reduced, so a reduction ofloss in light quantity is possible.

FIG. 4A, FIG. 4C, and FIG. 4D are diagrams that illustrate thehorizontal mirror set 212 in the present embodiment. FIG. 4B is adiagram of the horizontal mirror set 212 of a comparative example.

The configuration of the output mirrors 2120 of the horizontal mirrorset 212 in the present embodiment will be described with reference toFIG. 4A to FIG. 4D.

The 43 horizontal output mirrors 2120 arranged parallel to one anotherin the Z-axis direction are used as the horizontal mirror set 212. FIG.4A schematically shows part of the horizontal output mirrors 2120. Anormal line to each of the 43 horizontal output mirrors 2120 is inclinedat 61 degrees in the Y-Z direction within a plane including the Ydirection and the Z direction. Each horizontal output mirror 2120 hastwo types of reflection regions 2121, 2122 having different reflectancesand different transmittances. A half mirror having a reflectance ofabout 45% and a transmittance of about 45%, that is, the ratio betweenthe reflectance and the transmittance is about 1:1, is disposed in thefirst reflection region 2121 of the horizontal output mirror 2120,located close to the horizontal propagation part 211. On the other hand,a high-reflectance mirror having a reflectance of about 85% and atransmittance of lower than or equal to 1% is disposed in the secondreflection region 2122 of the horizontal output mirror 2120, located farfrom the horizontal propagation part 211. In other words, the upper halfof the horizontal output mirror 2120 in height (Y direction) is the halfmirror 2121, and the lower half is the high-reflectance mirror 2122.Thus, of beams coining from the horizontal propagation part 211, part ofincident beams to the half mirror 2121 are reflected to be deflectedtoward the vertical light guide part 22, and another part of theincident beams transmit through the half mirror 2121 and are thenreflected by the high-reflectance mirror 2122 of the subsequent outputmirror 2120 to be deflected toward the vertical light guide part 22. Inother words, when the horizontal output mirrors 2120 include first andsecond mirrors, light having transmitted through the first reflectionregion of the first mirror is reflected by the second reflection regionof the second mirror and enters the vertical light guide part, and lightreflected by the second reflection region of the first mirror directlyenters the vertical light guide part not by way of the second mirror. Atthis time, deflected beams deflected by the output mirrors 2120 towardthe vertical light guide part 22 have wider beam widths than the beamwidths of the propagating beams within the horizontal propagation part211. The beam widths of the propagating beams inside the horizontalpropagation part 211 are Wp1, Wp2, and Wp3, and the widths of thedeflected beams after being reflected by the horizontal output mirrors2120 are Wr1, Wr2, and Wr3. The widths of the beams after beingreflected by the horizontal output mirrors 2120 are constantly largerlike Wr1>Wp1, Wr2>Wp2, and Wr3>Wp3, and the beams reach the viewer's eyewith these beam widths, so the effect of expanding the pupil in thehorizontal direction is provided by the horizontal light guide part 21.

FIG. 4B shows the comparative example. A horizontal mirror set of thecomparative example differs from the configuration of the presentembodiment in that the entire region of each horizontal output mirror2120 is a high-reflectance mirror. Although deflected beams deflected bythe horizontal output mirrors 2120 are also expanded to be wider thanthe beam widths of propagating beams as in the case of the presentembodiment, there are many gaps (no beam portions) in the deflectedbeams, so there is a problem in uniformity in light quantity within thedeflected beams.

When the half mirror 2121 is disposed in part of each horizontal outputmirror 2120 as in the case of the present embodiment, propagating beamsare separated by the half mirror 2121 into reflected beams andtransmitted beams, so gaps that appear when the beam widths of thereflected beams are expanded are filled by the transmitted beams. Forthis reason, the high-reflectance mirror 2122 is disposed on thevertical light guide part side of each half mirror 2121, and beamshaving transmitted through the half mirrors 2121 reflect on thehigh-reflectance mirrors 2122 of the adjacent horizontal output mirrors2120 and fill the above-described gaps.

In this way, by splitting a beam entering each horizontal output mirror2120 into two beams and deflecting the beams toward the vertical lightguide part 22, not only the existing advantageous effect of expandingthe width of each of deflected beams but also the advantageous effect ofmaking the light quantity distribution in the expanded deflected beamsuniform is obtained.

Propagating beams totally reflected by the top surface 2113 of thehorizontal propagation part 211 reach the horizontal output mirrors2120. The first reflection region of each horizontal output mirror 2120is disposed on the horizontal propagation part top surface 2113 side ofthe second reflection region, that is, the first reflection region isdisposed closer to the top surface 2113 of the horizontal propagationpart 211 than the second reflection region. By adopting thisconfiguration, expansion of the pupil by deflected beams and uniformityin light quantity are achieved.

The horizontal output mirror 2120 of the present embodiment isconfigured such that the half mirror 2121 and the high-reflectancemirror 2122 are disposed one above the other on halves at the ratio of1:1; however, the ratio is not limited thereto. The ratio at which thehalf mirror 2121 and the high-reflectance mirror 2122 are disposed maybe 2:1, 3:1, 4:1, or the like. Furthermore, the half mirror 2121 may beentirely disposed. As compared to these arrangements, when the halfmirror 2121 and the high-reflectance mirror 2122 are disposed at 1:1, abeam that originates from light having transmitted through the halfmirror 2121 and reflected from the high-reflectance mirror 2122 isdisposed between beams reflected by the half mirrors 2121. Thisconfiguration is suitable for expanding the widths of beams, making thelight quantity distribution in the expanded beams uniform, and improvinglight usage efficiency. The half mirror 2121 is not limited to theconfiguration that the reflectance is 45% and the transmittance is 45%and may be an amplitude splitting mirror that splits amplitude. Forexample, when the transmittance is set so as to be higher than thereflectance by setting the reflectance to 41% and setting thetransmittance to 49%, the light quantity of a reflected beam from thehalf mirror is substantially equal to the light quantity of a beamhaving transmitted through the half mirror and reflected from thehigh-reflectance mirror, and the light quantity distribution in beamscan be corrected further uniformly. Even when the ratio between thereflectance and the transmittance is 2:1 or 1:2, the half mirror isusable with practically no problem.

Of the horizontal output mirrors 2120, no mirror follows the last mirror(the mirror farthest from the incident surface 2115) and has noeffective part, so the light quantity of a deflected beam is increasedby setting both the first region 2121 and the second region 2122 ashigh-reflectance mirrors.

The interval between any adjacent horizontal output mirrors 2120 ispreferably less than a pupil diameter 4 mm of the eye 5 and morepreferably less than or equal to 2 mm, that is, sufficiently less thanthe pupil diameter. However, when the interval between any adjacenthorizontal output mirrors 2120 is less than 0.5 mm, a numerical aperturereduces, and resolving power becomes problematic, so the interval Pbetween any adjacent horizontal output mirrors 2120 preferably takes thefollowing range.

0.5 mm≤P≤2.0 mm  Conditional Expression (2)

As shown in FIG. 1, when the viewer sees a display image, beams that arein charge of the left-side angle of view of the image exit from the leftside of the light guide plate 2, beams that are in charge of theright-side angle of view of the image exit from the right side of thelight guide plate 2, and both enter the viewer's eye.

As in the case of the present embodiment, when the horizontal mirror set212 is disposed between the horizontal propagation part 211 and thevertical light guide part 22, beams having larger propagation angles areused at locations near the incident surface 2115 (the left side of thelight guide plate 2 in FIG. 2), and beams having smaller propagationangles are used at locations far from the incident surface 2115 (theright side of the light guide plate 2 in FIG. 2).

In propagation inside the horizontal propagation part 211, totalreflection occurs on the front surface 2111, the rear surface 2112, andthe top surface 2113; however, the reflectance is lower than 100% at thebottom surface 2114 because reflection by the transmissive reflectionfilm occurs on the bottom surface 2114, and the light quantity ofpropagating light decreases according to the number of times ofreflection.

When the horizontal mirror set 212 is disposed between the horizontalpropagation part 211 and the vertical light guide part 22 as in the caseof the present embodiment, light usage efficiency is improved by makingthe number of times of reflection at each angle of view uniform andreducing the number of times of reflection on the bottom surface 2114 ofthe horizontal propagation part 211. In this way, it is advantageous inthat propagation angles and locations to be used can be set to asuitable relationship. In addition, different from the bottom surface2114 of the horizontal propagation part 211, no reflection occurs at abottom surface 2124 of the horizontal mirror set 212. Therefore, theregion of the bottom surface 2124 of the horizontal mirror set 212, fromwhich beams exit, is joined with the region of the vertical propagationpart 221, which beams enter, so the horizontal light guide part 21 andthe vertical light guide part 22 are easily unified. Thus, thepositional relationship between the horizontal light guide part 21 andthe vertical light guide part 22 is maintained with high accuracy, so agood image can be constantly displayed.

In this way, the configuration of the present embodiment is advantageousin improvement of light usage efficiency resulting from a reduction inthe number of times of reflection by the transmissive reflection filmand unification of the light guide plate 2 as compared to the case wherethe horizontal mirror set 212 is disposed on the top surface 2113 sideof the horizontal propagation part 211 as described in Japanese PatentApplication Laid-Open No. 2010-33316 or International Publication No.WO2015/076335. In addition, the configuration of the present embodimentis similarly advantageous as compared to the case where the horizontalmirror set 212 is disposed in the horizontal propagation part 211 andbeams finally reflected from the bottom surface of the horizontalpropagation part 211 are reflected by the horizontal mirror set 212 asin the case of Japanese Patent Application Laid-Open No. 2005-521099.

In the horizontal mirror set 212 of the present embodiment, the intervalbetween any adjacent two horizontal output mirrors 2120 is constantlyset to 1 mm equally, and the height (Y direction) is changed accordingto the position of the horizontal output mirror 2120. The horizontaloutput mirror 2120 near the incident surface 2115 of the horizontalpropagation part 211 is higher and becomes lower in height as theposition of the horizontal output mirror 2120 gets away from theincident surface 2115 (according to the distance in the Z direction).Since propagating beams totally reflected from the top surface 2113 ofthe horizontal propagation part 211 enter the horizontal output mirrors2120, a distance from the top surface 2113 of the horizontal propagationpart 211 is increased as the position of the horizontal output mirror2120 gets away from the incident surface 2115 of the horizontalpropagation part 211. This is because, as described above, the absolutevalue of the propagation angle of a propagating beam to be an effectivebeam reduces with a distance from the incident surface 2115 of thehorizontal propagation part 211, so the height of the horizontal outputmirror 2120 is lowered according to the absolute value of the associatedpropagation angle. The incident surface 2115 side of the horizontalpropagation part 211 is a region where propagating beams havingpropagation angles of ±45 degrees become effective beams, and thehorizontal output mirrors 2120 are set to be higher, that is, 3.0 mm,such that any gap between the adjacent beams reduces at the time whenthe propagating beams are deflected by the horizontal output mirrors2120. The center of the horizontal mirror set 212 is a region wherepropagating beams having median propagation angles ±32 degrees becomeeffective beams, and the horizontal output mirrors 2120 are set to amedium height, that is, 1.8 mm. The opposite side of the horizontalmirror set 212 from the incident surface is a region where propagatingbeams having smaller propagation angles ±19 degrees become effectivebeams, and the horizontal output mirrors 2120 are set to be lower, thatis, 1.2 mm. In this way, the height of the horizontal output mirror 2120is changed according to the propagation angle of a propagating beam thatbecomes an effective beam.

In FIG. 4A and FIG. 4B, the heights of the horizontal output mirrors2120 are all varied, and the heights are reduced linearly.Alternatively, the eights may be reduced in a stepwise manner byreducing the heights every several mirrors, or the heights may bereduced nonlinearly (for example, along a sine curve). Alternatively,those may be combined.

FIG. 4C and FIG. 4D are diagrams that illustrate a method of determiningthe heights of the horizontal output mirrors.

An upper limit of the height of each horizontal output mirror 2120 willbe described with reference to FIG. 4C.

In each of the horizontal output mirrors 2120 of the present embodiment,the first region 2121 is a half mirror, the second region 2122 is ahigh-reflectance mirror, and a beam 54 heading toward the boundarybetween the first region 2121 and the second region 2122 enters from thehorizontal propagation part 211 to the horizontal mirror set 212.

To set the number of half mirrors through which the beam 54 transmits toless than or equal to N, the height of the Nth last horizontal outputmirror 2120 from the horizontal output mirror 2120 of interest (towardthe incident surface side) is defined such that the beam 54 touches atop end of the Nth last horizontal output mirror 2120, and the upperlimit of the height of the horizontal output mirror 2120 of interest isset based on the defined height of the Nth last horizontal output mirror2120. The number of half mirrors through which a beam parallel to thebeam 54 and reflects on the second region 2122 transmits is preferablyless than or equal to three. An interval in the Z-axis direction fromthe boundary between the first region 2121 and the second region 2122 ofthe horizontal output mirror 2120 of interest to the top end of the Nthlast horizontal output mirror 2120 is denoted by Lu. The interval Lu isobtained from an interval PN between the horizontal output mirror 2120of interest and the Nth last horizontal output mirror 2120 and a widthLu1 that is half the width of the Nth last horizontal output mirror 2120at the time when the horizontal output mirror 2120 is disposed at aninclination angle of θ degrees. It is assumed that the beam 54 having apropagation angle w enters the boundary between the first region 2121and second region 2122 of the horizontal output mirror 2120 of interest.At this time, at the position of the top end of the Nth last horizontaloutput mirror 2120, the beam 54 passes at the height that is higher byLu×tanω from the height of the boundary between the first region 2121and second region 2122 of the horizontal output mirror 2120 of interest.Here, when the height of the Nth last horizontal output mirror 2120 isset to a height such that the Nth last horizontal output mirror 2120does not block the beam 54, the number of mirrors through which a beamparallel to the beam 54 and reflects on the second region 2122 transmitscan be set to less than or equal to N. In other words, the height of theNth last horizontal output mirror 2120 may be set such that H/2<Lu×tanω.This also applies to the horizontal output mirror 2120 of interest.

A lower limit of the height of each horizontal output mirror 2120 willbe described with reference to FIG. 4D.

A beam 55 enters a top end of the horizontal output mirror 2120, thebeam 55 is reflected by the first region 2121 of the horizontal outputmirror 2120, and the beam 55 passes between the horizontal output mirror2120 of interest and the last horizontal output mirror 2120. At thistime, when the height H of the horizontal output mirror 2120 is low fora pitch P1 of the horizontal output mirror 2120, an interval L1 betweenthe last horizontal output mirror 2120 and the reflected light 55increases, with the result that a gap occurs in deflected beams. Thelower limit of the height of the horizontal output mirror 2120 is setsuch that a gap greater than or equal to a predetermined width B is notformed in deflected beams at the horizontal output mirror 2120.Preferably, any gap in the deflected beams is set such that thepredetermined width B≤0.5 mm. In the drawing, L11 denotes the length ofthe horizontal output mirror 2120 in the Z direction, and L11=H/tanθ.L12 denotes a distance that the reflected light of the beam 55 travelsin the Z direction from the reflected position to the bottom surface2124 of the horizontal mirror set 212, and L12=H×tanα. Under suchconditions, the height H of each horizontal output mirror 2120 maysatisfy the relationship of the conditional expression (3).

${\left( {P_{1} - B} \right) \times \frac{\tan \mspace{14mu} \theta}{1 - {\tan \mspace{14mu} \alpha \times \tan \mspace{14mu} \theta}}} < H < \frac{4 \times P_{N} \times \tan \mspace{14mu} \omega \times \tan \mspace{14mu} \theta}{{\tan \mspace{14mu} \theta} - {\tan \mspace{14mu} \omega}}$

whereθ is the angle of the output mirror,ω is the propagation angle of an effective propagating beam in theoutput mirror of interest,α is a difference between the propagation angle of an effectivepropagating beam and the propagation angle of a beam at the center ofthe angle of view in the output mirror of interest,P1 is an interval between the output mirror of interest and the lastoutput mirror,PN is an interval between the output mirror of interest and the Nth lastoutput mirror, andB is an interval between a deflected beam and the output mirror (B≤0.5mm).

Conditional Expression (3)

In the conditional expression (3), N may be less than or equal to three.In the present embodiment, N is set to two. When the height exceeds theupper limit of the conditional expression, the number of times that abeam transmits through half mirrors increases, with the result that aloss in light quantity arises and becomes problematic.

In the present embodiment, the height of each horizontal output mirror2120 is determined by using the conditional expression (3); however, theconfiguration is not limited thereto. The height of each vertical outputmirror in the vertical mirror set 222 may be determined by using theconditional expression (3).

FIG. 5A shows an X-Y cross-sectional view of the vertical light guidepart in the display apparatus of the present embodiment.

As shown in FIG. 5A, the vertical light guide part 22 is made up of thevertical propagation part 221 and the vertical mirror set 222. Thevertical propagation part 221 is a flat plate, has a front surface 2211,a rear surface 2212, and a top surface 2213 as polished surfaces, andlight blocking films (light blocking parts) that block unnecessary lightare provided on the other three surfaces. The top surface 2213 of thevertical propagation part 221 is used as an incident surface, and beamsfrom the horizontal light guide part 21 enter from the incident surface.Of the front surface 2211 (second exit surface) of the verticalpropagation part 221, a region joined with the vertical mirror set 222is used as an exit region, and light having passed through at least partof the vertical propagation part 221 exits from the exit region.Propagating beams having entered the vertical propagation part 221 arepropagated in the vertical direction while repeating internal reflectionon two or less surfaces (the front surface 2211 and the rear surface2212) of the four surfaces parallel to the vertical direction of thevertical propagation part 221. The vertical mirror set 222 is disposedso as to face the rear surface 2212 (second reflection surface) of thevertical propagation part 221. In the vertical mirror set 222, theplurality of vertical output mirrors 2220 having a transmissivereflection surface that transmits part of incident beams and reflectspart of the incident beams is provided, and the vertical output mirrors2220 are arranged in the Y-axis direction so as to be inclined withinthe X-Y cross section and parallel to one another. The outer shape ofthe vertical mirror set 222 is a flat plate shape, and has a frontsurface 2221 and a rear surface 2222 as polished surfaces. The verticalpropagation part 221 and the vertical mirror set 222 each are widest inthe horizontal direction (Z-axis direction), second widest in thevertical direction (Y-axis direction), and narrowest in the depthdirection (X-axis direction). The vertical mirror set 222 is disposed onthe viewer's eye 5 side of the vertical propagation part 221, and thevertical propagation part 221 and the vertical mirror set 222 areunified by joining the front surface 2211 of the vertical propagationpart 221 with the rear surface 2222 of the vertical mirror set 222. Atransmissive reflection film is applied to a joint surface between thefront surface 2211 of the vertical propagation part 221 and the rearsurface 2222 of the vertical mirror set 222. The transmissive reflectionfilm transmits part of incident beams and reflects part of the incidentbeams.

The horizontal light guide part 21 and the vertical light guide part 22are unified by joining the bottom surface 2124 of the horizontal mirrorset 212 of the horizontal light guide part 21 shown in FIG. 3B with thetop surface 2213 of the vertical propagation part 221 of the verticallight guide part 22 shown in FIGS. 5A and 5B.

Propagating beams reflected by the horizontal output mirrors 2120 of thehorizontal light guide part 21 enter the top surface 2213 of thevertical propagation part 221, and propagate inside the verticalpropagation part 221 while repeating internal reflection between thefront surface 2211 and rear surface 2212 of the vertical propagationpart 221. At a portion joined with the rear surface 2222 of the verticalmirror set 222 in the front surface 2211 of the vertical propagationpart 221, because of the transmissive reflection film provided at thejoint surface, part of propagating beams transmit through thetransmissive reflection film and enter the vertical mirror set 222, andpart of the propagating beams reflect and propagate inside the verticalpropagation part 221. again.

The vertical mirror set 222 includes the 28 vertical output mirrors 2220disposed parallel to one another at an inclination angle of 58 degreesin the X-Y direction with respect to the rear surface 2212. Eachvertical output mirror 2220 reflects part of propagating beams havingentered the vertical mirror set 222 to deflect the beams toward thefront surface 2221 of the vertical mirror set 222 and transmits part ofthe propagating beams. Propagating beams having transmitted through thefirst vertical output mirror 2220 are reflected by the subsequentvertical output mirror 2220 to be deflected toward the front surface2221 of the vertical mirror set 222.

The front surface 2221 of the vertical mirror set 222 is parallel to therear surface 2212 of the vertical propagation part 221. When propagatingbeams directly enter the front surface 2221 of the vertical mirror set222 at angles at which the propagating beams have entered the verticalmirror set 22, the propagating beams are totally reflected because theincident angles exceed a critical angle. On the other hand, propagatingbeams deflected by the vertical output mirrors 2220 have smallerincident angles to the front surface 2221 of the vertical mirror set 222than the critical angle, and exit from the front surface 2221 of thevertical mirror set 222 toward the viewer's eye 5 (toward a thirddirection). Thus, an image is displayed by causing beams to enter theviewer's eye 5. An incident angle is an angle formed between theincident direction of a beam and a normal line to an incident surface.

In the vertical light guide part 22 as well, as in the case of thehorizontal light guide part 21, the width of each of deflected beams isexpanded so as to be wider than the width of each propagating beam withsuch a configuration that a propagating beam at one angle of view isdeflected by a plurality of the vertical output mirrors 2220.

FIG. 6 is a schematic diagram of the vertical output mirrors of thepresent embodiment.

The vertical output mirrors of the present embodiment will be describedwith reference to FIG. 6.

The 28 vertical output mirrors 2220 are used as the vertical mirror set222 of the present embodiment. In the present embodiment, the number ofthe horizontal output mirrors is greater than the number of the verticaloutput mirrors. This is because, of the angles of view for the viewer'seye, a horizontal angle of view is set so as to be greater than avertical angle of view and, in addition, the distance between theviewer's eye and the horizontal mirror set is longer than the distancebetween the viewer's eye and the vertical mirror set. With thisconfiguration, a good image can be constantly provided to the viewer.

FIG. 6 shows the six vertical output mirrors 2220 out of the 28 verticaloutput mirrors 2220. The vertical output mirrors 2220 of the presentembodiment each are a rectangular mirror having a long axis in the Zdirection. A polarization beam splitter (PBS) that is a polarizationsplitting mirror that splits a beam into polarized beams is used as eachvertical output mirror 2220 of the present embodiment. Morespecifically, a wire grid polarizer that is a type of form birefringentPBS using a sub-wavelength structure (SWS). The wire grid polarizer issuch that many dielectric wires 2226 (metal wires made of, for example,aluminum) are arranged in a grid at a pitch of less than or equal to thewavelength (about 100 nm) on an optical substrate 2225 (for example, aglass substrate). The wire grid polarizer has such characteristics thatthe wire grid polarizer transmits light (p-polarized light) of which theelectric field oscillates in a direction 2227 parallel to the wire grid(metal wires) and reflects light (s-polarized light) of which theelectric field oscillates in a direction perpendicular to the wire grid.In other words, the wire grid polarizer has such characteristics thatthe wire grid polarizer is a polarization beam splitter that allowsselection of the polarization direction of reflection or transmissionwith the orientation of the wire grid.

In the present embodiment, the vertical output mirrors 2220 are disposedsuch that the orientations of the wire grids of the vertical outputmirrors 2220 are alternately rotated by 90 degrees, so the orientationsof the wire grids of the adjacent vertical output mirrors 2220 aredisposed perpendicularly to each other. Specifically, a firstpolarization beam splitter that is one of the vertical output mirrors2220 has the orientation of the wire grid at 90 degrees with respect tothe long axis of the vertical output mirror 2220, and a secondpolarization beam splitter that is the adjacent vertical output mirror2220 has the orientation of the wire grid at 0 degrees. The verticaloutput mirror 2220 that a propagating beam has first entered splits thepropagating beam into a reflected beam and a transmitted beam, deflectsthe reflected beam toward the front surface 2221 of the vertical mirrorset 222, and the adjacent vertical output mirror 2220 reflects thetransmitted beam to deflect the beam toward the front surface 2221 ofthe vertical mirror set 222. Since the orientation of the wire grid ofthe first vertical output mirror 2220 and the orientation of the wiregrid of the adjacent vertical output mirror 2220 are perpendicular toeach other, the transmitted beam of the first vertical output mirror2220 is totally reflected by the adjacent vertical output mirror 2220.Light having transmitted through the first polarization beam splitter isreflected by the second polarization beam splitter and exits from thelight guide plate 2, while light reflected by the first polarizationbeam splitter exits from the light guide plate 2 not by way of thesecond polarization beam splitter. Therefore, a propagating beam splitsat 1:1 into a reflected beam and a transmitted beam at the first enteredvertical output mirror 2220, and the transmitted beam reflects at thesubsequently entered vertical output mirror 2220, so a single beam exitsfrom the two vertical output mirrors 2220 toward the viewer's eye. Thus,deflected beams are formed, and the width of each of the deflected beamsis expanded so as to be greater than the width of each propagating beam.When a dielectric multilayer PBS is used as each vertical output mirror2220 instead of a form birefringent PBS, the vertical output mirrors2220 can only be configured such that p-polarized light havingtransmitted through the first entered vertical output mirror 2220 alsotransmits through the subsequently entered vertical output mirror 2220.

There is also an example in which a half-wave plate is disposed in anoptical path having transmitted through a dielectric multilayer PBS;however, a dielectric multilayer PBS generally has high incident angledependency, and desired characteristics can be exercised only when theincident angle falls within an angular range near 45 degrees (about ±5degrees). A dielectric multilayer PBS also has high wavelengthdependency, and it is difficult to obtain good optical characteristics(reflectance, transmittance) over all the range in the visible lightrange (400 nm to 700 nm). Particularly, in a color image displayapparatus, light associated with three color spectrum ranges including ared spectrum (620 nm to 700 nm), a green spectrum (490 nm to 570 nm),and a blue spectrum (420 nm to 490 nm) are used, so wide-band wavelengthcharacteristics are desired. As in the case of the display apparatus ofthe present embodiment, in the light guide plate 2 configured such thatbeams having propagated inside the vertical propagation part 221transmit through the front surface 2211 of the vertical propagation part221 and enter the vertical mirror set 222, and the beams exit outward ofthe light guide plate 2 without passing through the vertical propagationpart 221 again, the incident angle to each vertical output mirror 2220tends to be a large angle exceeding 50 degrees. Practically, when beamspropagate inside the vertical propagation part 221, the beams each haveangles in two-dimensional directions, that is, the horizontal directionand the vertical direction, the incident angles of the propagating beamsto the vertical output mirrors 2220 of the vertical mirror set 222 are46 degrees to 68 degrees, which is a large angular range exceeding 45degrees over a wide range. Under such incident angle conditions, it isdifficult to ensure good optical performance with a dielectricmultilayer PBS. In addition, the incident angle in the verticaldirection varies in the range of 52 degrees to 61 degrees, the incidentdirection in the horizontal direction varies in the range of +13 degreesto −13 degrees, and it is difficult to constantly set the polarizeddirection to a desired angle when a wavelength plate is used,

However, a form birefringent PBS is able to change the polarizeddirection of transmitting polarized light or reflecting polarized lightby changing the orientation of the wire grid. Therefore, even when theincident angle to output mirrors is over a wide range as in the case ofthe present embodiment or a usage wavelength is over all the range inthe visible light range, a form birefringent PBS can be used as thevertical output mirror 20. Thus, p-polarized light having transmittedthrough the first entered vertical output mirror 2220 can be reflectedby the subsequent vertical output mirror 2220. In the presentembodiment, an organic electroluminescence (OLED) panel that emits lighthaving a low degree of polarization LED) is used as the display element4. However, when a liquid crystal panel, or the like, that emits lighthaving a high degree of polarization is used as the display element 4, adepolarizing plate may be provided in an optical path between thedisplay element 4 and the vertical mirror set 222. Specifically, adepolarizing plate be disposed between the display element 4 and theincident optical system 3 or between the incident optical system 3 andthe light guide plate 2.

FIG. 7 is a diagram that illustrates vertical output mirrors of thepresent embodiment.

FIG. 7 shows the five vertical output mirrors 2220.

A propagating beam having a small propagation angle ω is guided in thevertical light guide part 22, half of the light quantity reflects on thefirst reached vertical output mirror 2220, and the other half transmitstherethrough. The reflected propagating beam is deflected toward thefront surface 2221 of the vertical mirror set 222 and exits toward theviewer's eye. The transmitted propagating beam reflects on thesubsequent vertical output mirror 2220 to be deflected toward the frontsurface 2221 of the vertical mirror set 222 and exits toward theviewer's eye.

At this time, the beam having first transmitted through the firstvertical output mirror 2220 and reflected by the subsequent secondvertical output mirror 2220 and the beam having first entered the secondvertical output mirror 2220 and reflected by the second vertical outputmirror 2220 are arranged side by side. Thus, gaps between beams indeflected beams that exit toward the viewer's eye are reduced, and aconfiguration that the viewer is able to view at each angle of view witha uniform distribution in light quantity is achieved.

At this time, by disposing the vertical output mirrors 2220 such thatthe heights H and intervals P of the vertical output mirrors 2220satisfy the conditional expression (4), an appropriate configurationwith reduced gaps between beams in deflected beams is achieved.

${\left( {P_{1} - B} \right) \times \frac{\tan \mspace{14mu} \theta}{1 - {\tan \mspace{14mu} \alpha \times \tan \mspace{14mu} \theta}}} < H < {P_{2} \times \tan \mspace{14mu} \omega}$

whereθ is the angle of the output mirror,ω is the propagation angle of an effective propagating beam in theoutput mirror of interest,α is a difference between the propagation angle of an effectivepropagating beam and the propagation angle of a beam at the center ofthe angle of view in the output mirror of interest,P1 is an interval between the output mirror of interest and the lastoutput mirror,P2 is an interval between the output mirror of interest and the secondlast output mirror,B is an interval between a deflected beam and the output mirror (B≤0.5mm).

Conditional Expression (4)

When the height exceeds an upper limit, a propagating beam passesthrough three or more polarizers, and there occurs gaps in propagatingbeams that reach the output mirrors, and, as a result, gaps in deflectedbeams increase and become problematic. When the height becomes lowerthan a lower limit, the interval between a deflected beam and an outputmirror increases, and, as a result, gaps in deflected beams increase andbecome problematic.

The height becomes greater than an average diameter (about 4 mm) of thepupil (pupil) of the viewer's eye, a light quantity distribution due togaps in reflected beams is conspicuous and becomes problematic. When theheight is lower than the lower limit, the width of each reflected beambecomes too narrow, and the resolving power decreases, so it isproblematic.

A form birefringent polarizer, as compared to a dielectric multilayerpolarization beam splitter, has such characteristics that incident anglecharacteristics and wavelength characteristics are maintained at highperformance (reflectance, transmittance) in a wide range. In thevertical output mirrors 2220, the range of the incident angle is wideand is greater than or equal to 45 degrees and less than or equal to 70degrees, and the wavelength is also used in a wide band of greater thanor equal to 400 nm and less than or equal to 700 nm in visible light, sothe vertical output mirror 2220 takes advantage of a wide angle, wideband, and high performance of a form birefringent polarizer.

In this way, the width of each beam that exits from the light guideplate 2 is expanded, and the light quantity distribution in eachexpanded beam is made uniform. Thus, 15 mm of eye motion box (EMB) isensured at the position of the viewer's eye, and beams from a wide angleof view display image constantly enter the pupil of the viewer's eyeeven when the position of the pupil moves at the time of viewing aperipheral part of the display image, so a high-grade image can beprovided.

In FIG. 5B, in addition to the vertical light guide part 22 andpropagating beams in the vertical light guide part 22, shown in FIG. 5A,beams that enter the vertical light guide part 22 from the outside worldare represented by the alternate long and short dashed lines.

Beams from the outside world transmit through the rear surface 221.2 ofthe vertical propagation part 221, the front surface 2211, and the rearsurface 2222 of the vertical mirror set 222 in this order, furthertransmits through the vertical output mirrors 2220 and the front surface2221 of the vertical mirror set 222, and reaches the viewer's eye 5.Since a wire grid polarizer is used as each vertical output mirror 2220of the present embodiment, a polarized beam in a direction perpendicularto the array direction of the wire grid is able to transmit through thewire grid polarizer. Thus, the viewer is able to view the outside worldthrough the vertical light guide part 22, and an optical see-throughfunction is exercised.

In addition, in the region from the vertical output mirrors 2220 to theviewer's eye 5, an optical path of propagating beams from the displayelement 4 and an optical path of beams from the outside are overlappedin the same optical path, so an image from the display element 4 can bedisplayed in the outside world.

In this way, the display apparatus 1 of the present embodiment allowsthe viewer to view a wide-angle of view, high-grade display image bothin the horizontal direction and the vertical direction, allows theviewer to view the outside world by optical see-through, and allows theviewer to view both in a superposed manner.

The incident optical system 3 in the display apparatus 1 of the presentembodiment causes light coming from the display element 4 to obliquelyenter in two directions, that is, in the X-Y cross section and the Y-Zcross section, such that propagating beams are reflected by the topsurface 2113 of the horizontal propagation part 211 and the rear surface2212 of the vertical propagation part 221. Thus, the width of each beamto be irradiated to the viewer's eye is expanded in the two-dimensionaldirections, that is, the horizontal direction and the verticaldirection, and a wide angle of view is obtained in the two-dimensionaldirections.

In the display apparatus 1 of the present embodiment, a combination of ahalf mirror and a mirror is used as each horizontal output mirror 2120of the horizontal light guide part 21; however, the configuration is notlimited thereto. Only half mirrors or a combination of a plurality ofpolarizers of which the orientations of wire grids intersect with eachother may be used as the horizontal output mirrors 2120. Theconfiguration of the above-described vertical mirror set (theconfiguration that rotated wire grid polarizers are disposedalternately) may be applied as the configuration of the horizontalmirror set 212.

The wire grid polarizers are used as the vertical output mirrors 2220 ofthe vertical light guide part 22; however, the configuration is notlimited thereto. Half mirrors or combinations of a half mirror and amirror may be used.

In the display apparatus 1 of the present embodiment, the configurationthat the wire grid polarizers alternately rotated by 90 degrees aredisposed as the vertical output mirrors 2220 of the vertical light guidepart 22 is used. However, any adjacent wire grids are not limited to 90degrees-rotation arrangement and may be a rotation arrangement of 30degrees, 45 degrees, 60 degrees, 120 degrees, 135 degrees, or 150degrees. In short, rotation is preferably greater than or equal to 30degrees and less than or equal to 150 degrees; however, any adjacentwire grids just need to be oriented in different directions.

In the light guide plate 2 of the present embodiment, beams are guidedin the horizontal direction (Z direction) inside the horizontal lightguide part 21, and beams are guided in the vertical direction (Ydirection) inside the vertical light guide part 22. However, asdescribed in International Publication No. WO2015/076335, beams may beguided vertically (in the Y direction) inside the horizontal light guidepart 21, and beams may be guided horizontally (in the Z direction)inside the vertical light guide part 22. The light guide plate 2 isconfigured as in the case of the present embodiment is more desirablebecause the long axis direction of the vertical mirror set 222 coincideswith the horizontal direction and the visibility of the vertical mirrorset 222 for the viewer can be reduced. In the display apparatus 1 of thepresent embodiment, the propagation direction (first direction) of beamsin the horizontal propagation part 211 is perpendicular to thepropagation direction (second direction) of beams in the verticalpropagation part 221, and those directions are perpendicular to thedirection (third direction) in which beams exit from the light guideplate 2. However, those are not necessarily perpendicular to one anotherand just need to intersect with one another.

In the light guide plate 2 of the present embodiment, the horizontalmirror set 212 is disposed between the horizontal propagation part 211and the vertical propagation part 221. However, the horizontal mirrorset 212 just needs to be disposed between the top surface 2113 of thehorizontal propagation part 211 and the vertical propagation part 221,and, as in the case of Japanese Patent Application Laid-Open No.2005-521099, a mirror set may be disposed in the horizontal propagationpart 211. In this case, as in the case of Japanese Patent ApplicationLaid-Open No. 2005-521099, it is not desirable that beams finallyreflected by the bottom surface 2114 of the horizontal propagation part211 be reflected by the mirror set. As in the case of the presentembodiment, it is desirable that beams finally reflected by the topsurface 2113 of the horizontal propagation part 211 be reflected by themirror set. In other words, it is desirable that beams at the center ofthe angle of view (beams that exit parallel to the Y direction from themirror set) enter mirrors of the mirror set at incident angles greaterthan 45 degrees. With this configuration, beams having greater absolutevalues of the propagation angles can exit from the side closer to theincident surface 2115 of the horizontal light guide part 21 as effectivebeams, so a similar advantageous effect to that of the presentembodiment is obtained.

In the light guide plate 2 of the present embodiment, the verticalmirror set 222 is disposed between the vertical propagation part 221 andthe viewer's eye 5. However, the vertical mirror set 222 may be disposedbetween the rear surface 2212 of the vertical propagation part 221 andthe viewer's eye 5 (that is, on the side where beams exit from the lightguide plate 2 away from the rear surface 2212 of the verticalpropagation part 221), and a mirror set may be disposed in the verticalpropagation part 221. In this case as well, it is desirable that beamsfinally reflected by the rear surface 2212 of the vertical propagationpart 221 be reflected by the mirror set. In other words, it is desirablethat beams at the center of the angle of view (a beam that exitsparallel to the X direction from the mirror set) enter mirrors of themirror set at incident angles greater than 45 degrees.

Second Embodiment

FIG. 8 shows a display apparatus of a second embodiment to which thepresent invention is applicable.

The present embodiment differs from the first embodiment in that theconfigurations of the horizontal light guide part 21 and vertical lightguide part 22 are modified. Specifically, in the horizontal light guidepart 21, the height of the horizontal propagation part 211 is set so asto be greater than that of an aperture stop 33 of the incident opticalsystem 3 for the horizontal light guide part 21 and the transmissivereflection film disposed at the joint surface between the horizontallight guide part 21 and the horizontal mirror set 212 is omitted. In thevertical light guide part 22, the width of the vertical propagation part221 in the X-axis direction is greater than the width of the horizontalpropagation part 211 in the X-axis direction, and the transmissivereflection film disposed at the joint surface between the verticalpropagation part 221 and the vertical mirror set 222 is omitted.

FIG. 9A and FIG. 9B show horizontal light guide parts of comparativeexamples. FIG. 9C shows the horizontal light guide part of the presentembodiment.

The configuration of the horizontal light guide part in the presentembodiment will be described with reference to FIG. 9A, FIG. 9B, andFIG. 9C.

In FIG. 9A, FIG. 9B, and FIG. 9C, the horizontal light guide part 21made up of the horizontal propagation part 211 and the horizontal mirrorset 212, the incident optical system 3 made up of a projection lens 31and the connection part 32, and the display element 4 are schematicallyshown.

Beams that exit from pixels of the display element 4 are converted toparallel beams by the projection lens 31 and become beams having anglesof view appropriate for pixel positions of the display element 4. Thebeams coming from the projection lens 31 enter the connection part 32,part of the beams internally reflect at the connection part 32 and reachthe joint region 33 joined with the incident surface 2115 of thehorizontal propagation part 211, and another part do not internallyreflect at the connection part 32 and reach the joint region 33. Thus,two incident beams in a positive direction and a negative direction areformed with respect to the long axis Ax of the horizontal propagationpart 211. Each beam enters the horizontal propagation part 211 while thewidth is limited at the joint region 33 and becomes a propagating beam.In other words, the joint region 33 between the connection part 32 ofthe incident optical system 3 and the incident surface 2115 of thehorizontal propagation part 211 has the function of the aperture stop 33of the incident optical system 3. In other words, beams limited by theaperture stop 33 of the incident optical system 3 enter the horizontallight guide part 21.

As shown in FIG. 9A, in the comparative example, the entire surface ofthe left surface 2115 of the horizontal propagation part 211 is used tobe joined with the connection part 32 of the incident optical system 3,and the left surface 2115 of the horizontal propagation part 211 has thesame size as the aperture stop 33 of the incident optical system 3.Propagating beams having entered from the incident surface 2115 of thehorizontal propagation part 211 internally reflect on the top surface2113 and bottom surface 2114 of the horizontal propagation part 211 andpropagate inside the horizontal propagation part 211. At the incidentsurface 2115 of the horizontal propagation part 211, propagating beamsenter in two directions, that is, the positive direction and thenegative direction, with respect to the long axis Ax of the horizontalpropagation part 211 in the Y-Z direction, so the inside of thehorizontal propagation part 211 is filled with propagating beams. Thus,at the bottom surface 2124 of the horizontal mirror set 212, propagatingbeams are uniformly distributed on the side near the incident surface2115 of the horizontal propagation part 211.

In the horizontal light guide part 21 of the comparative example of FIG.9A, no transmissive reflection film is installed at the joint surfacebetween the bottom surface 2114 of the horizontal propagation part 211and the top surface 2123 of the horizontal mirror set 212, andpropagating beams in the horizontal propagation part 211 transmitthrough the joint surface and enter the horizontal mirror set 212. Atthis time, propagating beams in the horizontal propagation part 211propagate a distance Lp from the beginning position of the joint surfacebetween the bottom surface 2114 of the horizontal propagation part 211and the top surface 2123 of the horizontal mirror set 212, and thepropagating beams reach the horizontal mirror set 212 without any gap.

Reference sign We in FIG. 9A denotes a necessary beam region that isused at the center of the angle of view. The necessary beam region is awidth equivalent to the pupil diameter of the display apparatus, calledEMB, and usually a width of 6 mm to 15 mm is ensured.

However, in the comparative example of FIG. 9A, propagating beams reachpart of the necessary beam region We at the position of the bottomsurface 2124 of the horizontal mirror set 212. In this situation, beamshaving a sufficient width do not reach the viewer's eye, and there is aproblem that part of an image disappears.

FIG. 9B is a comparative example in which, in the horizontal light guidepart 21 of the comparative example of FIG. 9A, a transmissive reflectionfilm is disposed at the joint surface between the bottom surface 2114 ofthe horizontal propagation part 211 and the top surface 2123 of thehorizontal mirror set 212. The first embodiment is also this mode. Inthis case, part of propagating beams in the horizontal propagation part211 transmit through the joint surface between the bottom surface 2114of the horizontal propagation part 211 and the top surface 2123 of thehorizontal mirror set 212 and enter the horizontal mirror set 212, andanother part reflect and propagate inside the horizontal propagationpart 211 again. By repeating this action, propagating beams reach theterminal end 2116 of the horizontal propagation part 211, andpropagating beams are distributed over the entire range of thehorizontal mirror set 212. Therefore, deflected beams deflected by thehorizontal output mirrors 2120 are present in all the necessary beamregion We at the center of the angle of view, so beams having asufficient width reach the viewer's eye. However, the transmissivereflection film is disposed at the joint surface between the bottomsurface 2114 of the horizontal propagation part 211 and the top surface2123 of the horizontal mirror set 212, and reflects only part ofpropagating beams having entered the transmissive reflection film. Forexample, when the transmissive reflection film has a transmittance of25% and a reflectance of 65%, the light quantity of propagating beamsdecreases by 35% every reflection. Since the number of times ofreflection at the transmissive reflection film increases as thepropagation distance extends, a light quantity distribution commensuratewith the propagation distance occurs in deflected beams that exit fromthe horizontal light guide part 21, and the light quantity distributionis corrected to a low light quantity part by reducing the light quantityof a high light quantity part. Therefore, a loss in light quantityoccurs and becomes problematic.

FIG. 9C shows the horizontal light guide part of the present embodiment.

The horizontal propagation part 211 of the present embodiment isconfigured such that the height H (width in the Y-axis direction) of thehorizontal propagation part 211 is greater by Hc than the height Ha ofthe aperture stop 33 of the incident optical system 3. The length in theY-axis direction perpendicular to the bottom surface 2114 (extendedsurface (described later)) of the horizontal propagation part 211 isgreater than once and less than twice the width of the aperture in theY-axis direction of the aperture stop 33 of the incident optical system3. In other words, 0<Hc<Ha. The length of the horizontal propagationpart 211 in the Y-axis direction corresponds to the distance between twototal reflection surfaces (the top surface 2113 and the bottom surface2114) of the horizontal propagation part 211.

In the comparative examples of FIG. 9A and FIG. 9B, the height H of thehorizontal propagation part 211 is Ha.

In the horizontal light guide part 21 of the present embodiment, as inthe case of the comparative example of FIG. 9A, beams enter the jointregion 33, joined with the connection part 32 at the incident surface2115 of the horizontal propagation part 211, at angles (±ω) of twopositive and negative directions in the Y-Z cross section and becomepropagating beams. Propagating beams propagate inside the horizontalpropagation part 211 while totally reflecting on the bottom surface 2114and top surface 2113 of the horizontal propagation part 211. Thehorizontal light guide part 21 of the present embodiment has notransmissive reflection film at the joint surface between the bottomsurface 2114 of the horizontal propagation part 211 and the top surface2123 of the horizontal mirror set 212. For this reason, 90% or higher(more desirably, 95% or higher) propagating beams having entered theexit region of the bottom surface 2114 of the horizontal propagationpart 211 transmit through the joint surface and enter the horizontalmirror set 212. Therefore, after propagating beams enter the region inwhich the horizontal propagation part 211 is joined with the horizontalmirror set 212, the number of times of reflection is only once at thetop surface 2113 of the horizontal propagation part 211. Beams aredelivered to necessary regions by this number of times of reflection,that is, once.

When one cycle of propagation starts from the bottom surface 2114 of thehorizontal propagation part 211, reflects on the top surface 2113 of thehorizontal propagation part 211, and reaches the bottom surface 2114 ofthe horizontal propagation part 211 again, a propagation distance La perone cycle of propagation is given by the conditional expression (5).

La=H/tanω×2  Conditional Expression (5)

As expressed by the conditional expression (5), the propagation distanceLa per one cycle of propagation extends in proportion to the height H ofthe horizontal light guide part 21.

The horizontal light guide part 21 of the present embodiment isconfigured such that the height H (the width in the Y-axis direction) ofthe horizontal propagation part 211 is greater by Hc than the height Haof the aperture stop 33 of the incident optical system 3, so thepropagation distance is extended by 2×Hc/tanω. Thus, a propagating beamreaches the distal end (the farthest position from the incident surface2115 of the necessary beam region We) of the necessary beam region We ateach angle of view. FIG. 9C shows beams at the center angle of view asan example, With the configuration of the present embodiment,propagating beams are delivered to a position beyond the distal end ofthe necessary beam region We for the beams at the center angle of view.

To make propagating beams reach the distal end of the necessary beamregion We for each angle of view, the height H of the horizontalpropagation part 211 may be configured to be greater by Hc than theheight Ha of the aperture stop 33 of the incident optical system 3 sothat the conditional expression (6) is satisfied.

H = Ha + Hc${Hc} \geq \frac{{\left( {{Lo} + {We}} \right) \times \tan \mspace{14mu} \omega} - {2 \times {Ha}} - {Hm}}{2}$

whereH is the height (width in the Y-axis direction) of the horizontalpropagation part 211,Ha is the height of the aperture stop 33 of the incident optical system3,Hc is an amount by which the height of the horizontal propagation part211 is greater than the height of the aperture stop 33 of the incidentoptical system 3,Hm is the height of the horizontal mirror set 212,Lo is a distance from the most incident surface 2115-side position ofthe joint surface between the horizontal propagation part 211 and thehorizontal mirror set 212 to the most incident surface 2115-sideposition of the necessary beam region We,We is the width of the necessary beam region, andω is a propagation angle.

Conditional Expression (6)

On the other hand, when the height of the horizontal propagation part211 is set so as to be greater than the height of the aperture stop 33of the incident optical system 3, the inside of the horizontalpropagation part 211 is not filled with propagating beams. Althoughthere occurs propagating beam gaps where no propagating beams arepresent in the horizontal propagation part 211, when the propagatingbeam gaps are configured not to overlap the necessary beam region We ateach angle of view, only the above-described advantage is obtained. Evenwhen beams at the center angle of view shown in FIG. 9C are taken as anexample, propagating beam gaps are configured not to overlap thenecessary beam region We.

For this configuration, the configuration that the region where theheight H of the horizontal propagation part 211 is greater by Hc thanthe height Ha of the aperture stop 33 of the incident optical system 3is extended toward the connection part 32 beyond the joint surfacebetween the horizontal propagation part 211 and the horizontal mirrorset 212 is important. In FIG. 9C, an extended amount is Lh, and beamsreflected by the top surface of the connection part 32 of the incidentoptical system 3 are reflected by the extended surface (the surfacedisposed between the incident surface 2115 of the horizontal propagationpart 211 and the mirror set 212 in the horizontal direction and facingthe top surface 2113). Thus, the most leading position (closest to theincident surface 2115 of the horizontal propagation part 211) thatpropagating beams reach is located before the necessary beam region We.

At each angle of view, to keep propagating beam gaps out of thenecessary beam region, the extended amount Lh of a portion of thehorizontal propagation part 211 higher by Hc than the aperture stop 33of the incident optical system 3 may be configured to satisfy theconditional expression (7).

${Lh} \geq {\frac{{2 \times {Hc}} + {Ha} + {Hm}}{\tan \mspace{14mu} \omega} - {Lo}}$

whereHa is the height of the aperture stop 33 of the incident optical system3,Hc is an amount by which the height of the horizontal propagation part211 is greater than the height of the aperture stop 33 of the incidentoptical system 3,Hm is the height of the horizontal mirror set 212,Lo is a distance from the most incident surface 2115-side position ofthe joint surface between the horizontal propagation part 211 and thehorizontal mirror set 212 to the most incident surface 2115 position ofthe necessary beam region We, andω is a propagation angle.

Conditional Expression (7)

In this way, in the present embodiment, propagating beams at each angleof view are caused to reach the necessary beam region We for the angleof view, and propagating beam gap portions are configured not to overlapthe necessary beam region We.

In other words, a configuration that satisfies the conditionalexpression (6) and the conditional expression (7) at the same time isdesirable, and a configuration that the amount Hc by which the height ofthe horizontal propagation part 211 is greater than the height of theaperture stop 33 of the incident optical system 3 satisfies theconditional expression (8) is desirable.

(Lo+We)×tanω−2×Ha−Hm≤2×Hc≤(Lo+Lh)×tanω−Ha−Hm

whereH is the height (width in the Y-axis direction) of the horizontalpropagation part 211,Ha is the height of the aperture stop 33 of the incident optical system3,Hm is the height of the horizontal mirror set 212,Lo is a distance from the most incident surface 2115 position of thejoint surface between the horizontal propagation part 211 and thehorizontal mirror set 212 to the most incident surface 2115-sideposition of the necessary beam region We,Lh is the extended amount of a portion of the horizontal propagationpart 211, which is higher by Hc than the aperture stop 33 of theincident optical system 3,We is the width of the necessary beam region, andω is a propagation angle.

Conditional Expression (8)

As in the case of the present embodiment, when the height H of thehorizontal propagation part 211 of the horizontal light guide part 21 isgreater than the height of the aperture stop 33 of the incident opticalsystem 3, propagating beams at each angle of view reach the necessarybeam region with a smaller number of times of reflection.

In the present embodiment, the height of the horizontal propagation part211 of the horizontal light guide part 21 is set so as to be greater byHc than the height of the aperture stop 33 of the incident opticalsystem 3, and the extended amount Lh of the portion of the horizontalpropagation part 211, which is higher by Hc than the aperture stop 33 ofthe incident optical system 3, is appropriately set. Thus, theconfiguration that the number of times of reflection at the transmissivereflection surface is zero is achieved, so the display apparatus 1 witha reduced loss in light quantity is achieved. In other words, in thepresent embodiment, propagating beams having entered the horizontalpropagation part 211 are propagated in the horizontal direction by beinginternally reflected by three or more surfaces of the four surfaces (thefront surface 2111, the rear surface 2112, the top surface 2113, and thebottom surface 2114), parallel to the horizontal direction, of thehorizontal propagation part 211.

In the comparative example of FIG. 9B, beams at the center of the angleof view are reflected by not only mirrors disposed at a center portionincluding the necessary beam region We but also mirrors disposed at bothend portions, so there is a large loss in light quantity. However, inthe present embodiment of FIG. 9C, beams at the center of the angle ofview are reflected by only mirrors disposed at the center portionincluding the necessary beam region We and are not reflected by mirrorsdisposed at both end portions, so there is a small loss in lightquantity.

In the present embodiment, of both ends of the aperture of the aperturestop 33, the lower-side (extended surface-side) one end is disposed atthe same level with the bottom surface (extended surface) 2114, and theupper-side (reflection surface-side) other end is disposed below the topsurface (reflection surface) 2113. However, of both ends of the aperturestop 33, the upper-side (reflection surface-side) one end may bedisposed at the same level with the top surface (reflection surface)2113, and the lower-side (extended surface-side) other end may bedisposed above the bottom surface (extended surface) 2114. However, inthis case, the propagation distance can be extended by Hc/tanω.

FIG. 10 shows the vertical light guide part 22 of the presentembodiment.

In the present embodiment as well, the vertical light guide part 22 ismade up of the vertical propagation part 221 and the vertical mirror set222. The vertical mirror set 222 includes the plurality of verticaloutput mirrors 2220, a wire grid is used as each vertical output mirror2220, and the wire grids are disposed such that the orientations of thewire grids are rotated by 90 degrees in the adjacent vertical outputmirrors 2220. In the present embodiment, as shown in FIG. 10, a step isprovided in the vertical propagation part 221, and the vertical mirrorset 222 is disposed on the step.

The thickness T (width in the X direction) of the vertical propagationpart 221 of the present embodiment is greater than the thickness of thevertical propagation part 221 of the first embodiment. The thickness ofthe vertical propagation part 221 of the first embodiment is the same asthe thickness of the horizontal light guide part 21; however, thethickness T of the vertical propagation part 221 of the presentembodiment is greater by Tc than the thickness Ta of the horizontallight guide part 21. Thus, propagating beams in the vertical propagationpart 221. totally reflect on the rear surface 2212 of the verticalpropagation part 221, then enter the vertical mirror set 222, reflect onthe vertical output mirrors 2220 to be deflected, exit from the frontsurface 2221 of the vertical mirror set 222, and enter the viewer's eye5.

With an increased thickness of the vertical propagation part 221,propagating beams reach necessary portions where beams are used forangles of view only by totally reflecting once on the rear surface 2212of the vertical propagation part 221. Thus, propagating beams do notneed to be reflected by the joint surface between the verticalpropagation part 221 and the vertical mirror set 222, not only atransmissive reflection film is not used but also the verticalpropagation part 221 and the vertical mirror set 222 are unified, socost reduction is achieved.

Third Embodiment

FIG. 11A shows a front view of a third embodiment to which the presentinvention is applicable. FIG. 11B shows a side view.

The present embodiment differs from the second embodiment in that theconfigurations of the horizontal mirror set and vertical mirror set aremodified and the horizontal light guide part 21, the vertical lightguide part 22, and the connection part 32 of the incident optical system3 are unified.

As shown in FIG. 11A, in the present embodiment, the whole of the lightguide plate 2 is unified, and the horizontal output mirrors 2120 and thevertical output mirrors 2220 are embedded in a resin molded product.Specifically, the horizontal output mirrors 2120 and the vertical outputmirrors 2220 are made from glass, then put in a die, and the light guideplate 2 is molded from resin so as to cover the outer sides of themirrors 2120, 2220. This is so-called glass insert molding. Therefore,there is no definite boundary between the horizontal propagation part211 of the horizontal light guide part 21 and the horizontal mirror set212 unlike the second embodiment, and the output mirrors may be disposednear the propagation part within the range in which the output mirrorsdo not come into contact with propagating beams that have not reachedpredetermined output positions.

In the present embodiment, the height of each output mirror is changedportion by portion, and the interval (pitch) between any adjacent outputmirrors is also changed, so further flexible arrangement is possible.The interval of the output mirrors increases with a distance from theincident surface 2115 of the horizontal light guide part 21. Thus, gapsin deflected beams coining from the output mirrors are reduced, anddeflected beams having a further uniform light quantity distribution arecaused to enter the viewer's eye, so a high-grade image is displayed.

The light guide plate 2 of the present embodiment also includes thehorizontal light guide part 21 that guides light coming from theincident optical system 3 in the Z-axis direction and the vertical lightguide part 22 that guides the light in the Y-axis direction. Thehorizontal light guide part 21 includes the horizontal mirror set 212.The horizontal light guide part 21 reflects beams propagating inside thehorizontal light guide part 21 with the horizontal mirror set 212 andguides the beams to the vertical light guide part 22.

As in the case of the second embodiment, the incident surface 2115 ofthe horizontal light guide part 21 serves as the aperture stop 33 of theincident optical system 3. In addition, a distance in the Y-axisdirection between two total reflection surfaces of the horizontal lightguide part 21 is set so as to be longer than one and less than twice theaperture width in the Y-axis direction of the aperture stop 33.

As shown in FIG. 11B, the vertical light guide part 22 includes thevertical mirror set 222, deflects beams propagating inside the verticallight guide part 22 in the X-axis direction by reflecting the beams withthe vertical output mirrors 2220, and causes the beams to exit from thevertical light guide part 22 toward the viewer's eye 5.

In the present embodiment, both the height and interval of the pluralityof output mirrors are changed. Alternatively, when only the interval ofthe plurality of output mirrors is changed, gaps in deflected beams arereduced.

A human's eye turns its eyeball when views a different angle of view. Onthe other hand, there are gaps in deflected beams that exit from a lightguide plate, and the position and size of each gap vary depending on theangle of view.

When there are large gaps in beams that enter the viewer's eye, thelight quantity of beams that enter the pupil of the eye changes, so,even when an image having a uniform brightness is viewed, the imagelooks as bright parts and dark parts are dotted. A display image havingsuch quality that cannot be regarded as a good field of view as if ascene is seen through a wire screen.

On the other hand, in the display apparatuses 1 of the first to thirdembodiments, gaps in beams that enter the viewer's eye at all the anglesof view are narrowed, so differences between bright parts and dark partsat each angle of view reduce and are reduced to such a degree that theviewer is not annoyed. Thus, the display apparatuses are able toconstantly display good images.

The display apparatuses 1 of the first to third embodiments may beapplied to, for example, a head mounted display (including smartglasses,AR glasses, a scouter, and the like), a head-up display, a cellularphone display, a 3D display, and the like.

Fourth Embodiment

In the present embodiment, the display apparatus of the presentinvention is applied to smartglasses that are one example of a headmounted display.

FIG. 12 is a perspective view of the smartglasses 600 of the fourthembodiment to which the present invention is applicable.

The smartglasses 600 are a spectacle-type wearable terminal and is aterminal for so-called augmented reality (AR), which displays anactually viewing real world with various pieces of information added.

The smartglasses 600 include a frame and two display apparatus 1 a anddisplay apparatus 1 b. The frame includes a rim 61, a temple 62 a, and atemple 62 b. The display apparatus 1 a and the display apparatus 1 b arejoined with the bottom surface of the rim 61. The temple 62 a and thetemple 62 b are respectively joined with both sides of the rim 61. Thedisplay apparatus of any one of the first to third embodiments may beused as each of the display apparatus 1 a and the display apparatus 1 b.

Light from the display element (not shown) of the display apparatus 1 ais guided by the incident optical system 3 a and the light guide plate 2a to the right eye of a viewer who wears the smartglasses 600, and animage is seen by the right eye of the viewer. Similarly, light from thedisplay element (not shown) of the display apparatus 1 b is guided bythe incident optical system 3 b and the light guide plate 2 b to theleft eye of the viewer who wears the smartglasses 600, and an image isseen by the left eye of the viewer.

In the smartglasses 600 of the present embodiment, the direction inwhich the right and left eyes of the viewer are arranged coincides withthe horizontal direction (first direction) in which the horizontal lightguide part 21 propagates beams, and the direction perpendicular to therim 61 coincides with the vertical direction (second direction) in whichthe vertical light guide part 22 propagates beams. With thisconfiguration, the longitudinal direction of the mirrors of the verticalmirror set coincides with the direction in which the eyes of the viewerare arranged, so the visibility of the vertical mirror set of the vieweris reduced.

With the smartglasses of the present embodiment, a high-quality imagehaving a wide angle of view is displayed for a viewer who wears thesmartglasses.

The embodiments of the present invention are described above; however,the present invention is not limited to these embodiments. Variousmodifications and changes are possible within the scope of the presentinvention

For example, in the display apparatuses of the first to thirdembodiments, the display apparatus that expands the width of each beamin two-dimensional directions is described. Alternatively, theconfiguration of the horizontal mirror set or vertical mirror set of thefirst embodiment may be applied to a mirror set of a display apparatusthat expands the width of each beam in one-dimensional direction or theconfiguration of the horizontal propagation part or vertical propagationpart of the second embodiment may be applied to a propagation part of adisplay apparatus that expands the width of each beam in one-dimensionaldirection. Furthermore, the configuration of the mirror set of the thirdembodiment or the concept of unification of the third embodiment may beapplied to a propagation part of a display apparatus that expands thewidth of each beam in one-dimensional direction.

According to the present invention, a display apparatus that is able todisplay further high-quality images is provided.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

What is claimed is:
 1. A display apparatus comprising: a light guide element; and an incident optical system configured to cause light coming from a display element to enter the light guide element, wherein the light guide element includes a first light guide part configured to guide the light coming from the incident optical system a first direction and a second light guide part configured to guide the light coming from the first light guide part in a second direction intersecting with the first direction, the first light guide part has a plurality of mirrors disposed along the first direction and configured to guide the light to the second light guide part by reflecting the light, the plurality of mirrors includes a first mirror and a second mirror, each of the first and second mirrors has a first reflection region and a second reflection region having a higher reflectance than the first reflection region, and light having transmitted through the first reflection region of the first mirror enters the second reflection region of the second mirror.
 2. The display apparatus according to claim 1, wherein light having transmitted through the first reflection region of the first mirror is reflected by the second reflection region of the second mirror and enters the second light guide part, and light reflected by the second reflection region of the first mirror enters the second light guide part not by way of the second mirror.
 3. The display apparatus according to claim 1, wherein the first light guide part has a first reflection surface facing the plurality of mirrors, and the first reflection regions are closer to the first reflection surface than the second reflection regions.
 4. A display apparatus comprising: a light guide element; and an incident optical system configured to cause light coming from a display element to enter the light guide element, wherein the light guide element includes a light wide part configured to guide the light coming from the incident optical system in a first direction, the light guide part has a plurality of polarization beam splitters disposed along the first direction and configured to cause the light to exit from the light guide element by reflecting the light, the plurality of polarization beam splitters includes a first polarization beam splitter and a second polarization beam splitter, and light having transmitted through the first polarization beam splitter enters the second polarization beam splitter.
 5. The display apparatus according to claim 4, wherein light having transmitted through the first polarization beam splitter is reflected by the second polarization beam splitter and exits from the light guide element, and light reflected by the first polarization beam splitter exits from the light guide element not by way of the second polarization beam splitter.
 6. The display apparatus according to claim 4, wherein the plurality of polarization beam splitters comprises a form birefringent polarizer.
 7. The display apparatus according to claim 6, wherein the plurality of polarization beam splitters comprises a wire grid polarizer.
 8. The display apparatus according to claim 4, wherein each of the first and second polarization beam splitters is a wire grid polarizer, and an axial direction of a wire grid of the first polarization beans splitter and an axial direction of a wire grid of the second polarization beam splitter intersect with each other.
 9. The display apparatus according to claim 8, wherein an angle formed between the axial direction of the wire grid of the first polarization beam splitter and the axial direction of the wire grid of the second polarization beam splitter is greater than or equal to 30 degrees and less than or equal to 150 degrees.
 10. A display apparatus comprising: a light guide element; and an incident optical system configured to cause light coming from a display element to enter the light guide element, wherein the light guide element includes a first light guide part configured to guide the light coming from the incident optical system a first direction and a second light guide part configured to guide the light coming from the first light guide part in a second direction intersecting with the first direction, and at least one of the first light guide part and the second light guide part has a plurality of polarization splitting mirrors.
 11. The display apparatus according to claim 10, wherein the first light guide part has a plurality of amplitude splitting mirrors configured to guide the light to the second light guide part by reflecting the light, and the second light guide part has the plurality of polarization splitting mirrors configured to cause the light to exit from the light guide element by reflecting the light.
 12. A display apparatus comprising: a light guide element; and an incident optical system configured to cause light coming from a display element to enter the light guide element, wherein the light guide element includes a light guide part configured to guide the light coming from the incident optical system in a first direction, the light guide part is disposed along the first direction, the light guide part includes a propagation part configured to propagate the light coming from the incident optical system by internal reflection, and a plurality of wire grid polarizers disposed between the propagation part and an exit surface of the light guide part and configured to cause the light to exit from the light guide part by reflecting the light having propagated through the propagation part, the plurality of wire grid polarizers includes a first wire grid polarizer and a second wire grid polarizer, the light having transmitted through the first wire grid polarizer is reflected by the second wire grid polarizer and caused to exit from the light guide part, and the light reflected by the first wire grid polarizer is caused to exit from the light guide part not by way of the second wire grid polarizer.
 13. The display apparatus according to claim 12, wherein an axial direction of a wire grid of the first wire grid polarizer and an axial direction of a wire grid of the second wire grid polarizer intersect with each other.
 14. The display apparatus according to claim 13, wherein an angle formed between the axial direction of the wire grid of the first wire grid polarizer and the axial direction of the wire grid of the second wire grid polarizer is greater than or equal to 30 degrees and less than or equal to 150 degrees.
 15. The display apparatus according to claim 8, wherein an incident angle of the light that enters the first and second wire grid polarizers exceeds 50 degrees.
 16. The display apparatus according to claim 12, wherein light coming from the display element contains light corresponding to three color spectrum ranges including a red spectrum (620 nm to 700 nm), a green spectrum (490 rim to 570 nm), and a blue spectrum (420 nm to 490 nm).
 17. A display apparatus comprising: a light guide element; and an incident optical system configured to cause light coming from a display element to enter the light guide element, wherein the light guide element includes a first light guide part configured to guide the light coming from the incident optical system a first direction and a second light guide part configured to guide the light coming from the first light guide part in a second direction intersecting with the first direction, at least one of the first light guide part and the second light guide part has a plurality of wire grid polarizers, the plurality of wire grid polarizers includes a first wire grid polarizer and a second wire grid polarizer, the light having transmitted through the first wire grid polarizer is reflected by the second wire grid polarizer and caused to exit from the light guide part, and the light reflected by the first wire grid polarizer is caused to exit from the light guide part not by way of the second wire grid polarizer.
 18. The display apparatus according to claim 17, wherein the first light guide part has a plurality of wire grid polarizers configured to guide the light to the second light guide part by reflecting the light, and the second light guide part has the plurality of wire grid polarizers configured to cause the light to exit from the light guide element by reflecting the light.
 19. A head mounted display comprising: a display apparatus; and a frame, wherein the display apparatus includes a light guide element, and an incident optical system configured to cause light coming from a display element to enter the light guide element, the light guide element includes a first light guide part configured to guide the light coming from the incident optical system in a first direction and a second light guide part configured to guide the light coming from the first light guide part in a second direction intersecting with the first direction, the first light guide part has a plurality of mirrors disposed along the first direction and configured to guide the light to the second light guide part by reflecting the light, the plurality of mirrors includes a first mirror and a second mirror, each of the first and second mirrors has a first reflection region and a second reflection region having a higher reflectance than the first reflection region, and light having transmitted through the first reflection region of the first mirror enters the second reflection region of the second mirror. 